Swing-arm arrangement for a magnetic disc storage apparatus

ABSTRACT

A swing arm arrangement moves and positions a magnetic head over a surface of a rigid rotatable magnetic disc of a magnetic disc store. The arrangement includes a swing arm, a permanent magnetic stator having stator end plates, and a bearing arrangement having ball bearings. The swing arm, magnetic stator and ball bearings are mounted on a bearing pin. The bearings are arranged on the pin at opposite sides of the arm and are carried by the stator end plates.

This is a continuation of application Ser. No. 305,299, filed Sept. 24,1981.

BACKGROUND OF THE INVENTION

The invention relates to a swing-arm arrangement for moving andpositioning at least one magnetic head over at least one surface of atleast one rotatable rigid magnetic disc of a magnetic-disc storageapparatus for the storage and reproduction of data in digital form,which arrangement comprises: at least one swing arm which is pivotableabout a pivotal axis, the swing arms, if there is a plurality of sucharms, being spaced from each other and being stacked to form an assemblyof swing arms, which assembly is pivotable about said pivotal axis; atleast one flat control coil which is connected to the swing arm or tothe swing-arm assembly, the control coils, if there is a plurality ofsuch coils, being stacked to form an assembly of control coils which arespaced from each other; a permanent magnetic stator, comprising: astator frame, flat, axially magnetized permanent stator magnets, whichare connected to the stator frame and between which air gaps are formedfor each flat control coil, so that each control coil is movable in anaxial permanent magnetic field within an air gap between permanentstator magnets, and an iron stator end-plate on each side of the stator,which stator end-plates extend over the interposed control coils andstator magnets and on which the outermost stator magnets are mounted, sothat the axial permanent magnetic stator fields are closed via the ironstator end-plates; and a bearing arrangement for pivotably journallingthe swing arm or swing-arm assembly, which bearing arrangement comprisestwo ball-bearings, each having an inner race and an outer race, and apivotal bearing pin on which both the swing arm or swing-arm assemblyand the inner races of the two ball-bearings are mounted.

Magnetic disc storage equipment, comprising one or a plurality of rigidmagnetic discs, which each serve for the storage and reproduction ofdata in digital form on at least one side and generally on both sides,is employed on a large scale as peripheral equipment for data processingapparatus such as computers.

The magnetic discs rotate with a high speed, for example 3600revolutions per minute, and the magnetic heads, which are secured to theends of the carrying-arm arrangements, are moved over the surfaces ofthe magnetic discs to locations which are preselected by the dataprocessing apparatus in order to store data in a specific track on themagnetic disc or in order to reproduce data from said track. Thecarrying-arm arrangements comprise carrying arms which are eitherlinearly movable in a radical direction or which are pivotable about apivotal axis parallel to the axis of rotation of the magnetic discs. Theinvention relates to a carrying arm arrangement of the last-mentionedtype, herein referred to as a swing-arm arrangement. The magnetic headsshould be moved as fast as possible over the magnetic discs in order tominimize the time required for locating the correct track and storing orreproducing the data. The magnetic discs are manufactured with anextremely high degree of flatness. The magnetic heads float on a verythin film of air very close to the surfaces of the magnetic discs.

In many cases each magnetic head is secured to a resilient magnetic headcarrier in order to obtain the mobility which permits the magnetic headto float on the air film and in order to provide a resilient load whichexerts an accurately defined pressure on said head. In order to minimizethe external dimensions of magnetic-disc storage equipment, the variousmanufacturers attempt to arrange the magnetic discs as close as possibleto each other. The carrying-arm arrangements, especially when they areinterposed between two magnetic discs, should therefore be as flat aspossible and move as close as possible to the magnetic-disc surface. Itis obvious that the carrying arm should never touch the magnetic discsurface, because this would render the magnetic disc unserviceable.

Carrying-arm arrangements for magnetic-disc storage equipment shouldtherefore be manufactured with the necessary precision.

A swing-arm arrangement of the type mentioned in the opening paragraphis known from U.S. Pat. No. 4,150,407. The known swing arm arrangementcomprises one or more aluminium swing arms in the form of bifurcatedlevers which are pivotable about a pivotal axis disposed between twoends. Arranged near the one end of each swing arm is a magnetic headunit comprising the magnetic head and a resilient magnetic head carrier,which carrier is rigidly connected to the carrying arm. On the other endof the swing arm a control coil is arranged. Said coil belongs toelectromagnetically and electrically controllable actuating means bymeans of which it is possible to impart a pivotal movement about thepivotal axis of the swing arm to said arm, so as to enable the magnetichead to be moved over the magnetic disc in a substantially radialdirection.

In a version comprising a plurality of swing arms, said arms arearranged above and spaced from one another and they are combined to forman assembly of swing arms which are pivotable about the pivotal axis.Each swing arm carries a separate flat control coil, so that these coilsare also combined to form an assembly of control coils which are spacedfrom each other. The assembly of swing arms is journalled on a frame bymeans of a bearing arrangement, which comprises two ball-bearings and abearing pin on which the the inner races of the ball bearing are fixedby suitable means so as to be axially spaced from each other. The outerraces of the ball-bearings are fitted in a bearing housing which isscrewed to the deck of the magnetic-disc storage apparatus, acompression spring between the outer races eliminating the axial bearingplay. The control coils move in a permanent magnetic stator. Said statorcomprises a stator frame and a plurality of flat, axially magnetizedpermanent stator magnets, which are connected to the stator frame andbetween which air gaps are formed for each flat control coil, so thateach control coil is movable in an axial permanent magnetic field withinan air gap between permanent stator magnets. On each side of the stator,iron stator end plates are arranged which extend over the interposedcontrol coils and stator magnets and on which the outermost statormagnets are mounted, so that the axial permanent magnetic stator fieldsare closed via the iron stator end plates. Each control coil comprisesturns of an electrically conductive material wound onto a plastics coilformer, which forms one structural unit with the control coil by meansof a synthetic resin. The control coils are connected to the swing armsby clamping and gluing, on the ends of the swing arms which are remotefrom the magnetic heads.

The magnetic heads are moved over the magnetic discs with a high speedin a substantially diametrical direction, in order to minimize the timerequired for locating a track and storing or reproducing the data. Thus,the swing arm or swing-arm assembly is moved with jerky movements, whichgive rise to relatively great inertial forces. The bearing arrangementshould therefore be robust and stable.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a swing-armarrangement of the type mentioned in the opening paragraph, which isrobust and stable and which comprises a small number of parts, so thatit is also suitable for magnetic-disc stores of small dimensionsintended for large-scale use, for example as peripheral equipment forpersonal computers.

The invention is characterized in that the swing arm or the swing-armassembly is arranged on the bearing pin between the two ball-bearingsand that each of the stator end-plates of the permanent magnetic statorextends transversely of the pivotal axis of the swing arm or swing-armassembly, beyond the bearing pin, and carries one of the twoball-bearings.

The symmetrical arrangement of the bearings relative to the swing arm orswing-arm assembly results in minimal deformation of the bearing pin andensures that the bearings are equally loaded. The overall mountingheight of the swing-arm arrangement can be reduced and the constructionis compact because the bearings are mounted directly on the statorend-plates. This has the important additional advantage that theswing-arm arrangement always constitutes a unit, even before it isincorporated into the magnetic-disc storage apparatus.

One embodiment of the invention is of interest for swing-armarrangements in which a tacho-coil is connected to the swing arm orswing-arm assembly, which coil is movable in a permanent-magnetic fieldin order to generate an induction voltage which is a measure of thespeed of pivoting of the swing arm or swing-arm assembly. Thisembodiment, which provides a more compact construction, is characterizedin that at least one flat, axially magnetized permanent tacho-magnet isarranged on the outer side of a stator end-plate, so that the statorend-plate closes the axial magnetic field of said magnet on one side;that on the side of the stator end-plate on which the tacho-magnet(s) is(are) disposed the bearing pin has a free end, which extends through anopening in the relevant stator end-plate beyond said outer side; thatthe tacho-coil is flat; and that the flat tacho-coil is secured to saidfree end of the bearing pin and can move in the axial permanent magneticfield produced by the tacho-magnet(s). Preferably, use is made of afurther embodiment of the invention, which is characterized in that atacho end-plate is arranged at some distance from and parallel to thestator end-plate, thereby forming an air gap in which the tacho-coil canmove parallel to the flat tacho-magnet(s), so that the axial permanentmagnetic field of the tacho-magnet(s) is closed by a stator end-plate onthe one side and by the tacho end-plate on the other side.

A further embodiment, which contributes to a reduced mounting height ofa magnetic-disc storage apparatus, is characterized in that thetacho-magnets and the tacho-coil are disposed in a recess in the deck ofa magnetic-disc storage apparatus and that the tacho end-plate isarranged over the recess on that side of the deck which faces away fromthe stator end-plates.

One of the stator end-plates has an additional function in a furtherembodiment of the invention, which is characterized in that one of thetwo stator end-plates also constitutes a base plate of a frame of theswing-arm arrangement, with which the swing-arm arrangement can besecured to a deck of a magnetic-disc storage apparatus.

A simplified construction and a reduced cost price are obtained by meansof an embodiment of the invention, which is characterized in that thetwo stator end-plates comprise substantially identical flat plates whichare die-cut from a magnetizable sheet material; that the outer races ofthe ball-bearings are mounted in bearing housings on those sides of thestator end-plates which face the stator magnets, and that the statorend-plates are arranged at a distance from and parallel to each other bymeans of spacers.

Spurious fields at the sides of the permanent magnetic stator arereduced by the use of an embodiment of the invention, which ischaracterized in that the stator magnets extend in a directionsubstantially transverse to the direction of pivoting of the controlcoil(s), at least up to the edges of the stator end-plates.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention will now be described in more detail withreference to the drawing, in which:

FIG. 1 is a plan view of a magnetic-disc storage apparatus,

FIG. 2 is a side view of the magnetic-disc storage apparatus of FIG. 1,

FIG. 3 is an exploded view of a swing arm arrangement as used in themagnetic-disc storage apparatus shown in FIGS. 1 and 2,

FIGS. 4-6 represent the swing arm of the swing-arm arrangement indifferent positions,

FIG. 7 is a side view of a swing-arm arrangement comprising two swingarms, and

FIG. 8 is a plan view of the swing-arm arrangement of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The magnetic-disc storage apparatus of FIGS. 1 and 2 comprise a frame 1,to which a swing-arm arrangement 2 is rigidly secured. Two rigidmagnetic discs 3 and 4 are arranged coaxially on a common spindle 5 soas to be spaced from each other, and rotate about an axis of rotation 6.The swing-arm arrangement 2 and the magnetic discs 3 and 4 are coveredby a plastics cover 7. Said cover protects the magnetic discs 3 and 4against dust and other contaminatants. For the sake of brevity thoseparts of the magnetic-disc storage apparatus which are irrelevant to thepresent invention are not described and are not shown in the drawing,except for a box-shaped unit 8 which accommodates the electroniccircuitry necessary for the operation of the magnetic-disc storageapparatus.

The swing-arm arrangement in accordance with the invention will now bedescribed in more detail with reference to FIG. 3. The swing-armarrangement serves for moving and positioning four magnetic heads 9 to12 over two rotating rigid magnetic discs 3 and 4. Said magnetic headsare spaced from each other by a distance corresponding to the spacingbetween the magnetic discs 3 and 4 and are together arranged on a singleswing arm 14, which is pivotable about a pivotal axis 13. The magneticheads are together mounted on a single mounting device 15, which isformed with the faces, recesses and threaded holes necessary forlocating and mounting the magnetic heads on the swing arm. The mountingdevice 15 is rigidly connected to the swing arm 14 by gluing, using amethod as proposed in the applicant's previous application Ser. No.305,313 now U.S. Pat. No. 4,391,035 (herewith incorporated byreference).

Each of the magnetic heads 9 to 12 is arranged on a resilientmagnetic-head carrier, 9a to 12a respectively, which at its ends isprovided with a fixing part 9b to 12b respectively, which is equippedwith a fixing bush 9c to 12c respectively. The mounting device 15 isformed with a through-hole 16, in which the fixing bushes fit with someclearance. In order to secure a magnetic-head unit (comprising amagnetic head, the elastic head carrier and the fixing part) to themounting device 15 a slightly oversized ball is forced through therelevant fixing bush, so that the clearance between the fixing bush andthe through-hole is eliminated. Such magnetic-head units arecommercially available.

The center of gravity of the assembly comprising the mounting device 15and the magnetic heads 9 to 12 arranged thereon is disposedsubstantially in the plane of pivoting of the swing arm 14. This alsoapplies to the other parts of the magnetic-head units. However, theseparts have a substantially lower mass than the magnetic heads and themounting device.

The mounting device 15 comprises a plurality of projections 17, 18 and19 for mounting the magnetic heads 9 to 12 at regular distances fromeach other, in such a way that the projections constitute a comb. Themounting device comprises a plurality of parts 20, 21 and 22, which aredetachably secured to each other and which each comprise a projection ofthe comb. The parts 20 and 22 are secured to the central part 21 bymeans of bolts 23 and 24. The part 21 is glued to the swing arm 14,using the previously mentioned method, before the magnetic heads 10 and11 are connected to the projection 18 by means of the fixing bushes 10cand 11c. The magnetic heads 9 and 12 are connected to the projections 17and 19 of the parts 20 and 22 before said parts are connected to thecenter part 21 by means of the bolts 23 and 24. This facilitatesmounting of the vulnerable magnetic-head units on the mounting device15.

The swing arm comprises a first end 25 and a second end 26. The firstend 25 is remote from the pivoted axis 13. The magnetic heads 9 to 12are connected to the swing arm near the first end 25. The swing-armarrangement comprises a permanent magnetic stator 27 having flatpermanent stator-magnets 28 and 29 which are spaced from each other andbetween which an air gap 30 is formed, see FIG. 2. In said air gap thereis arranged a flat control coil 31 of an electrically conductivematerial, which coil is connected to the swing arm 14. The swing arm 14is pivotably journalled by means of a bearing arrangement 32. The flatcontrol coil 31 is arranged in a recess 33 of the swing arm 14. Theswing arm has been die-cut from an aluminium sheet, the recess 33 beingformed during the die-cutting operation. The bearing arrangement 32 issituated near the second end 26 of the swing arm and the control coil 31is arranged between the first end 25 and the second end 26 of the swingarm.

The swing arm is manufactured from a single flat piece of sheet materialand the flat control coil 31 has a thickness dimension which issubstantially equal to the thickness dimension of the sheet materialfrom which the swing arm is manufactured. The recess 33 in the swing armhas a shape which corresponds to the shape of the outer circumference ofthe control coil 31, so that said coil fits in said recess withclearance.

The control coil is glued in the swing arm 14 and is attached to thewall of the recess 33 by means of a film of glue, which is not visiblein FIG. 3. The control coil is situated in the plane of the swing arm,so that the swing arm with the control coil glued therein constitutes aflat unit of substantially constant thickness. The turns 34 of thecontrol coil are made of an electrically conductive material and arewound onto a central flat plastics coil former 35. The electricallyconductive material is not formed by an elongate copper wire, as iscustomary for control coils, but by an elongate aluminium strip 36having a width dimension equal to the thickness "d" of the coil andhaving a thickness dimension which is substantially smaller. The gluefor connecting the control coil 31 to the wall of said recess 33 hasbeen mixed with aluminium powder in order to ensure a satisfactory heattransfer between the coil and the sheet material of the swing arm.

The two outermost magnetic heads 9 and 12 of the stack of magnetic heads9 to 12 are shielded from spurious magnetic fields by mu-metal shields37 and 38, which are located at the outside beyond the respectivemagnetic heads and which are connected to the swing arm 14 via themounting device 15. The shields are formed with openings 39 and 40 andtogether with the parts 20 and 22 of the mounting device 15 they areconnected to the central part 21 of the mounting device by means ofbolts 23 and 24 respectively. On the lower shield 38, an integratedsemiconductor circuit 41 is mounted for processing signals from themagnetic heads 9 to 12. Thus, said signals can be amplified before theyare applied to the signal processing sections of the magnetic-discstorage apparatus. The semiconductor circuit 41 is mounted on a flexibleplastics strip 43 provided with electrically conductive tracks 42, whichstrip is secured to the shield 38 at a first end 44. Near a second end45, the plastics strip is connected to a stationary connector on theframe 1 of the magnetic-disc storage apparatus via a multi-poleconnector 46. Between said first and second ends 44 and 45, the plasticsstrip 43 comprises a freely movable portion 47 which does not impede themovements of the swing arm 14.

The bearing arrangement 32 for pivotably journalling the swing armcomprises a first ball bearing 48 and a second ball bearing 49, havinginner races 50 and 51 and outer races 52 and 53 respectively. The twoinner races 50 and 51 are fixed on a bearing pin 54, axially spaced fromeach other, by means of a circular clip 55 and a nut 56. The swing armis formed with an opening 57 for the bearing pin 54. On each side of theswing arm, rings 58 and 59 are disposed which retain the swing armbetween the inner races 50 and 51 for the ball bearings 48 and 49. Theouter races 52 and 53 of the ball bearing engage with bearing-housingmeans, which comprise a first and a first second bearing housing 60 and61 respectively. Axial clearance between the outer races 52 and 53 ofthe ball bearings is eliminated in that they are axially loaded by meansof pressure spring means in the form of a cup spring 62 which isdisposed near the outer race 52 on top of the upper ball bearing 48. Theball bearings are sliding fits in the bearing housings 60 and 61 and thecup spring 62 urges the ball bearings axially towards each other. Eachbearing housing comprises a length of extruded tube with a centralthrough-hole 63 for the outer races 52 and 53 of the two ball-bearings48 and 49 and three parallel through-holes 64 of smaller cross-section,which are situated around the central hole 63. The bearing housings 60and 61 are secured by means of self-tapping screws 65, which are fittedinto said holes 64.

The permanent magnetic stator 27 comprises a stator frame with two ironstator end plates 66 and 67, one on each side of the stator, whichstator end plates extend over the interposed control coil 31 and thestator magnets 28 and 29. Said magnets are glued onto the stator endplates. The stator magnets are axially magnetized in the direction ofthe pivotal axis 13 of the swing arm 14. The stator magnet 28 comprisestwo zones 28a and 28b which are oppositely polarized. The magnet 29 alsocomprises two oppositely polarized zones 29a and 29b. At the side facingthe control coil 31, the zone 28a is polarized oppositely to the zone29a and the zone 28b oppositely to 29b, so that the parts of the controlcoil 31 between the permanent stator magnets are disposed in permanentmagnetic fields of opposite polarity. The axial permanent magneticfields are closed via the two iron end-plates 66 and 67. Instead ofintegral stator magnets 28 and 29, it is obviously also possible toemploy a plurality of separate magnets. As an example, the stator magnet28 may comprise two parts, the zone 28a belonging to the one statormagnet and the zone 28b to the other stator magnet. The end plates 66,67 extend transversely of the pivotal axis 13, intersect the axis 13 andfurther extend in a direction generally toward the remote end of theswing arm 14. The end plates 66 and 67 of the permanent magnetic stator27 also extend transversely of the pivotal axis 13 of the swing arm 14beyond the bearing pin 54, and the bearing housings 60 and 61 aresecured to the stator end-plates 66 and 67 by means of the self-tappingscrews 65. Thus, the stator end-plates 66 and 67 also constitute theframe plates for the bearing arrangement 32. In addition to the twostator end-plates 66 and 67, the stator 27 comprises three spacers 68,69 and 70. By means of three bolts 71, 72 and 73 and associated nuts 74to 76, the assembly comprising the stator end-plates 66 and 67 and thethree spacers 68 to 70 are combined to form a rigid unit, constitutingthe stator frame of the permanent magnetic stator. Since the bearinghousings 60 and 61 are secured to said stator frame the stator framealso constitutes a frame for the complete swing-arm arrangement, thestator end-plate 67 also serving as the base plate by means of which thecomplete swing-arm arrangement can be mounted on the deck 77 of themagnetic-disc storage apparatus. The means for connecting the swing armarrangement 2 to the deck 77 are not shown, but will generally comprisescrew means.

The embodiment of the swing-arm arrangement shown in the drawing isequipped with a tacho-coil 78, which is connected to the swing arm 14and which is movable in a permanent magnetic field in order to generatean induction voltage which is a measure of the speed of pivoting of theswing arm 14. For this purpose, permanent tacho-magnets 79 and 80 arearranged on the outer side of the stator end-plate 67, which magnets aremagnetized axially and oppositely in the direction of the pivotal axis13. Instead of two magnets, a single flat magnet may be used with zonesof opposite polarization. The stator end-plate 67 also serves forclosing the axial magnetic fields produced by the two tacho-magnets 79and 80 on one side. On the side of the stator end plate 67 the bearingpin 54 comprises a free end 81, which extends through an opening 82 insaid stator end-plate beyond the outer side thereof. The tacho-coil 78,which is flat like the control 31, is secured to the free end 81 of thebearing pin 54 by means of a nut 83 and can move in a permanent magneticfield produced by the tacho-magnets 79 and 80. At some distance from thestator end-plate 67 there is arranged an iron tacho end-plate 84parallel thereto. The tacho coil 78 moves parallel to the flat tachomagnets 79 and 80, leaving an air gap between the stator end-plate 67and the tacho end-plate 84, so that the axial permanent magnetic fieldof the tacho-magnets is closed by the stator end-plate on one side andthe tacho end-plate on the other side. The tacho end-plate 84 is securedto the underside of the deck 77 by means of four self-tapping screws 85to 88, but may alternatively be secured to the stator end plate 67 bymeans of separate spacer means. The tacho-magnets 79 and 80 as well asthe tacho-coil 78 are disposed in a recess 89 of the deck 77.

The two stator end-plates 66 and 67 comprise substantially identicalplates which are die-cut from a flat magnetizable sheet material. Thus,they can be manufactured cheaply using simple means because only onetype of stator end plate needs to be manufactured. The requirementsimposed on the manufacturing accuracy are not stringent, so that afterdie-cutting the stator end plates need not be subjected to any machiningoperation. The stator magnets 28 and 29 extend in a direction which issubstantially transverse to the direction of pivoting of the controlcoil 31, slightly beyond the edges of the stator end-plates 66 and 67respectively, see also FIG. 1.

There is provided a stop 90, which with opposite sides 91 and 92cooperates with the respective sides 93 and 94 of the wall of a recess95 in the swing arm 14. The sides 91 and 92 of the stop 90 limit thepivotal movement of the swing arm between a first and a second position.See FIGS. 4 and 5, which represent the swing arm 14 in the first orinner position and the second or outer position respectively. The stop90 is made of rubber and is movable between an operating position, seeFIGS. 4 and 5, and a maintenance position, see FIG. 6. The stop, whichis made entirely of elastic rubber, comprises a rotatable stop cam whichis a moderately tight fit on the spacer 68. For this purpose, the stophas an opening 96 of a diameter which is slightly smaller than the outerdiameter of the spacer 68. The opening is eccentric, so that the stopcam is eccentrically rotatable between the operating position and themaintenance position. In the maintenance position, the stop cam has beenrotated through 90°.

In this position, the sides 93 and 94 of the wall of the recess 95cooperate with opposite sides 97 and 98 of the stop cam. Said sides aresituated nearer each other than the sides 91 and 92, so that formaintenance purposes the swing arm 14 can be pivoted through such anextended range that the magnetic heads 9 to 12 will be situated besidethe surface of the magnetic discs 3 and 4. This position is alsoemployed during assembly of the magnetic disc apparatus to enable themagnetic heads to be mounted on the magnetic disc apparatus withoutbeing damaged.

A second embodiment of the invention comprising two swing arms will nowbe described with reference to FIGS. 7-8. This second embodiment willonly be described briefly because it bears great resemblance to theswing-arm arrangement of FIGS. 3-6. Parts corresponding to those of thefirst embodiment bear the same reference numerals but augmented by 100.

Between the swing arms 114A and 114B, a cylindrical intermediate portion200 is arranged. The stator in addition comprises a flat permanentmagnet 201, which cooperates with the coils of the two swing arms. Thismagnet is glued in an aluminium stator plate 202. The stator end-plates166 and 167 are provided with lugs 203 and 204 respectively, whichproject slightly sideways. The stator end-plate 202 is connected to thetwo stator end-plates 166 and 167 by means of the bolt 171, two furtherbolts 205 and spacers 206 and 207.

Many embodiments are possible within the scope of the invention. Thecontrol coils may, for example, be arranged on the other side of thepivotal axis. The ball-bearings may be accommodated in recesses of thestator end-plates, so that these plates also function as bearinghousings. Alternatively, separate bearing housings may be arranged onthe outer sides of the stator end-plates.

What is claimed is:
 1. A swing arm arrangement for moving andpositioning a magnetic head over a surface of a rigid rotatable magneticdisc of an apparatus for the storage and reproduction of digital data,which arrangement comprises:a swing arm pivotal about an axis and havingan end remote from the pivotal axis; a flat control coil connected tothe swing arm; a permanent magnetic stator includinga stator frame, aplurality of flat, axially magnetized permanent stator magnets connectedto the stator frame, the magnets forming an air gap for the control coiland being arranged such that the coil is movable in an axial permanentmagnetic field within the air gap formed between the permanent statormagnets, the stator frame including a pair of iron stator end platessubstantially defining two outer sides of the permanent magnetic stator,the plates extending over the control coil and the stator magnets, themagnets being mounted on the plates; and a bearing arrangement,associated with the swing arm, for pivotally journalling the swing arm,the bearing arrangement comprising two ball bearings each having aninner race, the bearing arrangement further comprising a pivotal bearingpin coaxial with the pivotal axis, the swing arm and the inner races ofthe ball bearings being mounted on the bearing pin,characterized in thatthe swing arm is arranged between the two ball bearings, and each of thestator plates extends transversely of the pivotal axis, intersects theaxis and further extends in a direction generally toward the remote endof the swing arm, each plate carrying one ball bearing.
 2. A swing armarrangement as claimed in claim 1, wherein one of the end plates forms abase plate for mounting a swing arm arrangement to a deck of themagnetic disc storage apparatus.
 3. A swing-arm arrangement (2) asclaimed in claim 1, in which a tacho-coil (78) is connected to the swingarm (14), which coil is movable in a permanent magnetic field in orderto generate an induction voltage which is a measure of the speed ofpivoting of the swing arm (14), characterized in thatat least one flat,axially magnetized permanent tacho-magnet (79) is arranged on the outerside of the stator end-plate (67), so that the stator end-plate (67)closes the axial magnetic field of said magnet on one side, on the sideof the stator end-plate (67) on which the tacho-magnet is disposed, thebearing pin (54) has a free end (81) which extends through an opening(82) in the stator end-plate beyond said outer side, the tacho-coil isflat, and the flat tacho-coil is secured to said free end (81) of thebearing pin (54) and can move in the axial permanent magnetic fieldproduced by the tacho-magnet (79).
 4. A swing-arm arrangement as claimedin claim 3, characterized in that a tacho end-plate (84) is arranged atsome distance from and parallel to the stator end-plate (67), therebyforming an air gap in which the tacho-coil can move parallel to the flattacho-magnet, so that the axial permanent magnetic field of thetacho-magnet is closed by the stator end-plate on the one side and bythe tacho end-plate on the other side.
 5. A swing-arm arrangement asclaimed in claim 4, characterized in that the tacho-magnet (79) and thetacho-coil (78) are disposed in a recess (89) in a deck (77) of amagnetic-disc storage apparatus, and the tacho end-plate (84) isarranged over the recess (89) on that side of the deck (77) which facesaway from the stator end-plates (66, 67).
 6. A swing-arm arrangement asclaimed in claim 2, characterized in thatthe stator end-plates (66, 67)comprise substantially identical flat plates which are die-cut from amagnetizable sheet material, outer races (52, 53) of the ball-bearings(48, 49) are mounted in bearing housings (60, 61) on those sides of thestator end-plates which face the stator magnets (28, 29), and the statorend-plates are arranged at a distance from and parallel to each other bymeans of spacers (68, 70).
 7. A swing-arm arrangement as claimed inclaim 1, characterized in that the stator magnets (28, 29) extend in adirection substantially transverse to the direction of pivoting of thecontrol coil (31), at least up to the edges of the stator end-plates(66, 67).